Swift中的简单服务，是否仍然存在，仅在前台? [英] Simple service in Swift, persists, foreground only?

问题描述

我只是想让某事运行

• 每说20秒
• 仅在应用程序为前台时显式显示(当后台运行时显式不运行)
• 很显然，如果您不必担心应用程序进入和退出前景，那会更加优雅
• 这个问题，我惊讶地发现scheduleRepeating，在模拟器中，当应用程序在后台运行时，它保持运行:这并没有使我确信它明确地显示了不会在某些设备上在后台运行
• 这个问题，我发现在尽可能多的世代/操作系统上进行测试的设备上，scheduleRepeating恼人的将(在某些情况下还是所有情况下)只能运行一次 当应用进入后台时.就是说:一旦应用程序进入后台，它就会再运行一次".吸.

• every say 20 seconds
• simply only when the app is foreground (explicitly not run when background)
• obviously, it would be more elegant if you don't have to bother following the app going in and out of foreground
• The issue, I was amazed to learn with scheduleRepeating that, in the simulator, it keeps running when the app is in background: that doesn't give me confidence that it explicitly won't run in background on (some? whatever?) devices
• The issue, I discovered that on a device, testing with as many generations / OS as possible, scheduleRepeating annoyingly will (in some? all? cases) run one time only when the app goes into background. That is to say: it runs "one more time" once the app goes to background. Suck.

因此要重复一遍:在iOS中，如何有一个简单的服务每20秒运行一次，并且仅在应用程序处于前台时运行，并且没有大惊小怪..理想情况下，您无需重新启动在应用程序的生命周期中对其进行检查，检查或任何其他操作...

So to repeat: in iOS how to have a simple service that runs every 20 seconds, and, only runs when the app is in a foreground, and, it is fuss-free .. ideally you don't have to restart it, check it or anything during the life of the app...

真正做到这种简单事情的最佳方法是什么?

really what is the best way to do such a simple thing?

这是我的(看似)可行的解决方案，非常小巧.在iOS中肯定有一种内置的方式或类似的方式来做这种明显的事情?

This is my (seemingly) working solution, which is inelegant. Surely there is a built-in way, or something, to do such an obvious thing in iOS??

open class SomeDaemon {

    static let shared = SomeDaemon()
    fileprivate init() { print("SomeDaemon is running") }
    var timer: DispatchSourceTimer? = nil
    let gap = 10   // seconds between runs

    func launch() {

        // you must call this from application#didLaunch
        // harmless if you accidentally call more than once
        // you DO NOT do ANYTHING on app pause/unpause/etc

        if timer != nil {

            print("SomeDaemon, timer running already")
            return
        }

        timer = DispatchSource.makeTimerSource(flags: [], queue: DispatchQueue.main)
        timer?.scheduleRepeating(deadline: .now(), interval: .seconds(gap))
        timer?.setEventHandler{ self. doSomeThing() }
        timer?.resume()
    }

    private func doSomeThing() {

        if UIApplication.shared.applicationState != .active {

            print("avoided infuriating 'runs once more in bg' problem.")
            return
        }

        // actually do your thing here
    }
}

推荐答案

幕后:

它不是华丽的，但是效果很好.

Behind the scenes:

It isn't gorgeous, but it works pretty darn well.

struct ForegroundTimer {
    static var sharedTimerDelegate: ForegroundTimerDelegate?
    static var sharedTimer = Timer()

    private var timeInterval: Double = 20.0

    static func startTimer() {
        ForegroundTimer.waitingTimer.invalidate()

        var wait = 0.0
        if let time = ForegroundTimer.startedTime {
            wait = timeInterval - (Date().timeIntervalSince1970 - time).truncatingRemainder(dividingBy: Int(timeInterval))
        } else {
            ForegroundTimer.startedTime = Date().timeIntervalSince1970
        }
        waitingTimer = Timer.scheduledTimer(withTimeInterval: wait, repeats: false) { (timer) in
            ForegroundTimer.sharedTimerDelegate?.timeDidPass()
            ForegroundTimer.sharedTimer = Timer.scheduledTimer(withTimeInterval: timeInterval, repeats: true, block: { (timer) in
                ForegroundTimer.sharedTimerDelegate?.timeDidPass()
            })
        }
    }

    static func pauseTimer() {
        ForegroundTimer.sharedTimer.invalidate()
    }

    private static var startedTime: TimeInterval?
    private static var waitingTimer = Timer()
}

protocol ForegroundTimerDelegate {
    func timeDidPass()
}

上面的代码可以按原样使用.当然，您可以将timeInterval设置为所需的任何时间间隔.

This code above is ready to use as-is. Of course you can timeInterval to whatever time interval you want.

在AppDelegate.swift中，具有以下两种方法:

In AppDelegate.swift, have these two methods:

func applicationDidBecomeActive(_ application: UIApplication) {
    ForegroundTimer.startTimer()
}

func applicationDidEnterBackground(_ application: UIApplication) {
    ForegroundTimer.pauseTimer()
}

然后，具有您要针对计时器实现ForegroundTimerDelegate进行监听"的任何类，并且它是必需的方法timeDidPass().最后，将该类/self分配给ForegroundTimer.sharedTimerDelegate.例如:

Then, have whatever class you want to 'listen' for the timer implement ForegroundTimerDelegate, and it's required method, timeDidPass(). Finally, assign that class/self to ForegroundTimer.sharedTimerDelegate. For example:

class ViewController: UIViewController, ForegroundTimerDelegate {
    func viewDidLoad() {
        ForegroundTimer.sharedTimerDelegate = self
    }

    func timeDidPass() {
        print("20 in-foreground seconds passed")
    }
}

希望这会有所帮助！

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